Where the end or active portion of a tool or working electrode is moved automatically under numerical control, it has been common practice to establish from a drawing numerical values corresponding to the successive positions of such a member to be moved. Thus, a required path of movement has been determined from the drawing whereupon the successive positions have been identified thereon. The successive numerical values corresponding to these positions are then recorded on a store medium such as punched tapes, cards or magnetic tapes for reproduction during the actual course of displacement of the member. When the path is drawn on an intricate three-dimensional surface, it is apparent that the number of numerical values or the amount of numerical data may be increased prohibitively and requires a great deal of time for not only the preparation but also the transfer, i.e. recording and reproduction, of the required numerical data.
While a computer has also been used sometimes in conjunction with the conventional NC process, its use has in practice been limited either to the preparation of these numerical values for recording and reproduction or to execute, during the data reproduction stage, a linear or curvilinear interpolation process which does not materially serve to reduce the time and effort required.
In the conventional computation of numerical values of successive positions in conjunction with the NC process, it should also be noted that positions lying on an intersection of two different three-dimensional surfaces have been found to be complex and troublesome to compute. While the use of a computer certainly eased such computations, the computer needed to be large-sized and capable of high-speed operation but success was nevertheless quite limited. Even a high-speed computer, the time required for handling the complete process for many an actual displacement operation has been quite unsatisfactorily long.